A reduced surface field (RESURF) MOS transistor is adopted for a laterally diffused metal-oxide-semiconductor field effect transistor (LDMOSFET, LDMOS transistor or LDMISFET, simply referred to as “LDMOS” hereinafter). A structure in which a thick oxide film is formed on a front surface of a semiconductor substrate and a drain-side edge of a gate electrode is arranged on the oxide film, thereby reducing the field intensity below the drain-side edge of the gate electrode has been studied.
For example, Japanese Unexamined Patent Application Publication No. 2011-003608 (Patent Document 1) discloses an LDMOS transistor in which a p+ buried region having a p type impurity concentration higher than that of a p− epitaxial region is formed between an n+ buried region and the p− epitaxial region.
Also, Japanese Unexamined Patent Application Publication No. 2011-514675 (Patent Document 2) discloses an N channel LDMOS formed in an isolated P type region. This N channel LDMOS includes an N+ drain region, a gate, a gate oxide film, an N+ source region and a P+ body contact region. Then, a deep P type region is arranged below the source region.
In addition, Japanese Unexamined Patent Application Publication No. 2006-505136 (Patent Document 3) discloses a RESURF transistor including an electrically floating semiconductor region above a semiconductor substrate and a P type body region and an N type drift region located above the electrically floating semiconductor region. Then, when a reverse bias is applied, a semiconductor region between the N type drift region and the electrically floating semiconductor region is depleted.